The field of the present invention relates to shock absorbers of the type that are adjustable. More particularly, the present invention relates to shock absorbers that are adjustable in the compression stage only.
Shock absorbers are widely use to dampen shocks experienced, for example, when a recreational vehicle such as a snowmobile travels over rough terrain. In the case of the snowmobile, the shock absorbers are positioned between the chassis and the slide frame around which an endless track rotates to propel the vehicle or in the front suspension between the skis and the chassis. The shock absorbers allow the slide frame or the skis to compress towards the chassis at a controlled rate.
Shock absorbers typically have a cylindrical wall sealed between two end caps creating a cavity in which a fluid is contained to provide hydraulic damping. The interior of the cylinder is separated into two sections by a piston, which contains passages therethrough to increase or decrease the fluid flow between each section of the cylinder. A shock rod, which passes through the rod eye end cap, is attached to the piston at one end and to the vehicle at its other end. Normally the shock rod is attached to the vehicle through a rod eye, hence the name xe2x80x9crod eye end capxe2x80x9d. The other end cap is secured to the slide frame, in the case of a snowmobile. The shock rod and the shock body, which includes the cylindrical wall and both of the end caps, move in relation to one another to dampen any forces applied thereto.
Passages are formed through the longitudinal axis of the piston and connect one section of the cylinder, the shock body, to the other. Portions of these passages are covered with leaf valves while the remainder of the openings serve as a bypass with no restriction other than the diameter of the passages. These bypass portions function primarily when the speed of the piston is low, i.e.: 0 to 0.3 m/s. The xe2x80x9cspeedxe2x80x9d of a piston is the rate at which the piston and the shock body move with respect to one another when an external force is applied thereto. In certain shock absorbers, once the speed of the piston increases above 0.3 mls, the fluid pressure increases enough to open the leaf valves. This may vary depending on the intended use of the shock absorber.
A typical xe2x80x9cPiston Speed vs. Compression Forcexe2x80x9d graph, such as the one depicted in FIG. 8, may be divided into three sections: low, medium and high. The low speed curve corresponds to speeds from about 0 m/s to approximately 0.3 m/s. The medium speed range corresponds to speeds from about 0.3 m/s to 1 m/s, and the high-speed range corresponds to speeds higher than about 1 m/s.
Because the lower speeds do not have an adverse effect on the driver or the driving performance of the snowmobile, the medium and high-speed ranges tend to be where attention is focused when designing a shock absorber. Since the fluid inside the shock body travels across the piston through the bypass portions during the low speed range, any adjustments to the valves have little or no effect on the low speed functioning of the shock.
Conventional adjustable hydraulic shock absorbers, such as the one shown in U.S. Pat. No. 5,542,509, are adjustable in both the compression and in the rebound stages. The compression stage occurs when the vehicle encounters uneven terrain and the force generated by the encounter is transferred to the piston of the shock absorber. The rebound stage is the traveling of the piston back to its steady state position, normally by the aid of a coil spring. The coil spring, which compresses when the vehicle encounters uneven terrain, will force the vehicle away from the ground and generate the force required to return the shock absorber to its steady state position during the rebound stage. The force exerted by the spring is usually quite low, because the force of the spring only needs to be high enough to overcome the force of gravity and not the forces associated with uneven terrain.
U.S. Pat. No. 5,542,509 describes a twin-tube shock absorber with an adjustment mechanism. The adjustment mechanism is a screw cam, which is screwed into a bore in the endcap of the shock absorber. The screw cam abuts the spring seat for the compression or blow off valve spring. Tightening or loosening the screw cam, relative to the endcap, increases or decreases the pre-load of the compression valve spring, thereby adjusting the manner in which the shock absorber responds to compression forces applied thereto.
In the case where a shock absorber is used in a recreational vehicle, such as a snowmobile, the compression stage of the shock absorber has a greater effect on the vehicle than the rebound stage. As mentioned, this is due to the fact that the weight of the vehicle is relatively small and, therefor, the rebound force required is equally small. This stands in dramatic contrast to the very high compressive forces that the shock absorber may experience as the recreational vehicle traverses uneven terrain.
Additionally, different riders prefer different response characteristics of the shock absorbers on their vehicles. For example, those engaged in snowmobile racing prefer a xe2x80x9cstifferxe2x80x9d shock than those enjoying a leisurely excursion on the outdoor snowmobile trail or through an ungroomed rural setting.
A need has developed for a simple, effective mechanism that permits adjustment of the compression response of a shock absorber such that the recreational vehicle including the shock absorber may satisfy several different riding preferences. The prior art does not address this deficiency.
It is, therefore, an object of the present invention to provide a simple, cost-effective, reliable, adjustable shock absorber with improved characteristics.
It is another object of the present invention to provide a shock absorber that is adjustable in compression in medium and high piston speed ranges.
It is still an object of the present invention to provide an adjustable shock absorber that is adjustable electrically using a solenoid.
It is yet another object of the present invention to provide an adjustable shock absorber, which is adjustable hydraulically.
It is still another object of the present invention to provide an adjustable shock absorber, which is adjustable mechanically.
In furtherance of these objects, one aspect of the present invention is to provide an adjustable shock absorber having a shock rod with a longitudinal axis. A shock body is disposed around the shock rod and is slidable along the longitudinal axis of the shock rod. The interior of the shock body defines a first fluid chamber. A piston is disposed on the shock rod in such a manner that the piston sealingly engages with the interior of the shock body. The piston includes channels passing therethrough in communication with the first fluid chamber. At least one valve is positioned to be in communication with the channel to control fluid movement through the channel. A support, movable longitudinally on the shock rod, is disposed adjacent to the valve. An adjustment mechanism is provided for altering the position of the movable support to adjust the fluid movement through the channel.
Yet another aspect of the of the present invention is to provide an adjustable shock absorber including a solenoid, which alters the fluid movement through the channel in the piston.
According to yet another aspect of the present invention, a snowmobile is provided that includes a chassis. An engine is disposed on the chassis. A steering column is attached to at least one ski for steering the snowmobile over the snow. An endless track is disposed under the chassis and is operatively connected to the engine for propelling the snowmobile. The snowmobile includes an adjustable shock absorber. The adjustable shock absorber has a shock rod with a longitudinal axis. A shock body is disposed around the shock rod and is slidable along the longitudinal axis of the shock rod. The shock body defines a first fluid chamber. A piston is disposed on the shock rod in such a manner that the piston sealingly engages with interior of the shock body. The piston includes channels passing therethrough in communication with the first fluid chamber. At least one valve is in communication with the channel to control fluid movement through the channel. A support, movable longitudinally on the shock rod, is disposed adjacent the valve. An adjustment mechanism is provided for altering the position of the movable support to adjust the fluid movement through the channel.
Yet another aspect of the present invention is to provide a snowmobile with an adjustable shock absorber that includes a solenoid which alters the fluid movement through the channel in the piston.
The foregoing objects are not meant to limit the scope of the present invention. To the contrary, still other objects of the present invention will become apparent from the description that follows.